Update repo to use current Sphinx and openstackdocstheme versions:
* update requirements
* update conf.py to correctly set variables
* update tox.ini to use python3
There's no .md file in here, so change links. Looking at the used links,
these are all external links and thus sphinx cannot test whether they
work. Use internal links so that all links work - and work even after
This shows up as e.g.:
WARNING: unknown document: install-maas.html
Update tox.ini so that these are hard errors.
Remove dead requirement oslosphinx, it's not needed anymore here since
openstackdocstheme is used.